1. Field of the Invention
The present invention relates to an apparatus for reduced-pressure epitaxial growth and to a method of controlling the apparatus. More specifically, the invention relates to an apparatus for reduced-pressure gaseous phase epitaxial growth maintaining, in a predetermined range, the pressure in the rotary mechanical portion of a susceptor on which is placed a semiconductor substrate such as silicon wafer and to a method of controlling the apparatus.
2. Prior Art
A reduced-pressure DVD apparatus is usually used for epitaxially growing a single crystal thin film on a semiconductor substrate such as silicon wafer in gaseous phase.
The conventional apparatus for reduced-pressure epitaxial growth will be described in detail with reference to FIG. 2. The apparatus for reduced-pressure epitaxial growth includes a processing furnace 1, a susceptor 9 that rotates while placing thereon a semiconductor wafer 8, a rotary mechanical portion 5 for rotating the susceptor 9, a gas introduction pipe 11 for introducing a film-forming gas into the processing furnace, a gas exhaust pipe 10 for exhausting the film-forming gas, a pressure adjusting valve 4 provided in the gas exhaust pipe 10 for exhausting the film-forming gas, a pressure gauge 2 for detecting the pressure in the processing furnace, and an arithmetic/control unit 3 for executing the arithmetic operation based on the pressure that is detected to control the opening degree of the pressure adjusting valve 4 provided in the gas exhaust pipe 10 that exhausts the film-forming gas, so that the pressure in the processing furnace assumes a proper value.
Being constituted as described above, the pressure in the processing furnace 1 is controlled to assume a predetermined value, and the semiconductor wafer 8 is processed under the predetermined pressure.
Further, a purging gas introduction pipe 6 and a purging gas exhaust pipe 7 are arranged for the rotary mechanical portion 5 disposed in the lower part of the processing furnace 1, and an inert gas such as argon gas is introduced through the purging gas introduction pipe 6 to purge the interior of the rotary mechanical portion 5. After having purged the interior of the rotary mechanical portion 5, the inert gas is exhausted through the purging gas exhaust pipe 7. Thus, the interior of the rotary mechanical portion 5 is purged with the inert gas to suppress metallic contamination generated by the rotary mechanical portion 5 from migrating into the processing furnace 1 and, hence, to suppress the processing furnace and the semiconductor wafer from being contaminated with metallic contaminants.
In the conventional apparatus for reduced-pressure epitaxial growth, however, the pressure in the rotary mechanical portion has not been controlled.
In the conventional apparatus, therefore, when a relationship between the pressure (p1) in the processing furnace and the pressure (p2) in the rotary mechanical portion is, for example, p1 greater than p2, the reactive gas (film-forming gas) used in the processing furnace enters into the rotary mechanical portion to contaminate machine parts such as bearings constituting the mechanical portion and the encoder, making it necessary to frequently clean the rotary mechanical portion. On the other hand, when the relationship between p1 and p2 is p1 less than p2 contrary to the above, the purging gas that has passed through the rotary mechanical portion and is contaminated with metals infiltrates into the processing furnace, and the semiconductor wafer being processed is often contaminated with metals.
In order to decrease the frequency for cleaning the interior of the rotary mechanical portion as much as possible and to minimize the metallic contamination upon the semiconductor wafer being processed, maintaining p1=p2 would be effective without, however, proper and explicit ranges for the two. Even when p2 could be set to lie in a proper range, a change in the pressure p1 in the processing furnace due to a change in the flow rate of gas in the processing furnace causes the pressure p2 to lie outside the proper range, and the above-mentioned harmful influence occurs.
In the conventional apparatus, it can be contrived to prevent the above-mentioned harmful influence by completely sealing the processing furnace from the rotary mechanical portion. In practice, however, a high sealing performance is not accomplished due to the structure of the apparatus; i.e., the rotary shaft for rotating the susceptor is extending into the processing furnace from the rotary mechanical portion. If it is attempted to maintain a highly reliable sealing performance, a new problem arouses in that the structure of the apparatus becomes complex and the apparatus itself becomes expensive.
The present invention was accomplished in view of the above technical assignment inherent in the prior art, and has an object of providing an apparatus for reduced-pressure gaseous phase epitaxial growth by suppressing contamination upon the machine parts constituting the rotary mechanical portion and suppressing contamination upon the semiconductor wafer by maintaining the pressure in the rotary mechanical portion to lie within a particular range, and a method of controlling the above apparatus.
In order to solve the above technical assignment, the apparatus for reduced-pressure epitaxial growth according to the present invention comprises a processing furnace, a susceptor disposed in the processing furnace and rotates while placing a semiconductor wafer thereon, a rotary mechanical portion for rotating the sucseptor, a gas introduction pipe for introducing a film-forming gas into the processing furnace, and a gas exhaust pipe for exhausting the film-forming gas, the apparatus for reduced-pressure epitaxial growth further comprising a purging gas introduction pipe for purging the interior of the rotary mechanical portion, a purging gas exhaust pipe for exhausting the gas introduced through the purging gas introduction pipe, a pressure adjusting valve provided in the purging gas exhaust pipe, a pressure gauge for detecting the pressure in the rotary mechanical portion, and an arithmetic/control unit for executing an arithmetic operation based upon the detected pressure and for controlling the opening degree of the pressure adjusting valve provided in the purging gas exhaust pipe, so that the pressure in the rotary mechanical portion assumes a proper value.
As described above, the apparatus for reduced-pressure epitaxial growth according to the present invention includes the pressure adjusting valve provided in the purging gas exhaust pipe, the pressure gauge for detecting the pressure in the rotary mechanical portion, and the arithmetic/control unit for executing an arithmetic operation based upon the detected pressure and for controlling the opening degree of the pressure adjusting valve provided in the purging gas exhaust pipe, so that the pressure in the rotary mechanical portion assumes a proper value. Therefore, the apparatus for reduced-pressure epitaxial growth of the invention makes it possible to control the pressure in the rotary mechanical portion to lie in a desired range, that could not be controlled by the conventional apparatus.
That is, the apparatus for reduced-pressure epitaxial growth according to the present invention suppresses the infiltration of the film-forming gas (reactive gas, etc.) into the rotary mechanical portion from the processing furnace, decreasing the contamination in the rotary mechanical portion. Besides, infiltration of the purging gas into the processing furnace from the rotary mechanical portion is suppressed, decreasing contamination for the semiconductor wafer.
Here, it is desired to provide a pressure gauge for detecting the pressure in the processing furnace, a pressure gauge for detecting the pressure in the rotary mechanical portion, and an arithmetic/control unit for executing the arithmetic operation based on the pressure in the processing furnace and the pressure in the rotary mechanical portion that are detected and for controlling the opening degree of the pressure adjusting valve provided in the purging gas exhaust pipe, so that the pressure in the rotary mechanical portion assumes a proper value.
Thus, provision is made of the pressure gauge for detecting the pressure in the processing furnace, the pressure gauge for detecting the pressure in the rotary mechanical portion, and the arithmetic/control unit for executing the arithmetic operation based on the pressure in the processing furnace and the pressure in the rotary mechanical portion that are detected and for controlling the opening degree of the pressure adjusting valve provided in the purging gas exhaust pipe, so that the pressure in the rotary mechanical portion assumes a proper value. Accordingly, even when the pressure in the processing furnace changes, the pressure in the rotary mechanical portion can be adjusted to assume a proper value.
It is desired that the apparatus for reduced-pressure gaseous phase epitaxial growth includes a pressure adjusting valve provided in the gas exhaust pipe for exhausting the film-forming gas, a pressure gauge for detecting the pressure in the processing furnace, and an arithmetic/control unit for executing the arithmetic operation based on the pressure in the processing furnace and the pressure in the rotary mechanical portion that are detected and for controlling the opening degree of the pressure adjusting valve provided in the purging gas exhaust pipe, so that the pressure in the rotary mechanical portion assumes a proper value.
In the method of controlling the apparatus for reduced-pressure epitaxial growth of the invention for solving the above-mentioned technical assignment, further, when the pressure in the processing furnace is denoted by p1 and the pressure in the rotary mechanical portion by p2, then a ratio of p2 to p1 (P=p2/p1) is controlled to lie in a range 0.9xe2x89xa6Pxe2x89xa61.0.